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;     1 

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emprelnte. 

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1.    1 

:    2 

i     ^ 

j.    1 

2 

3 

4 

5 

6 

,^r'!^5'"'-'■■: 


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,  •'  WA^ 


V 


[From  the  Proceedings  of  the  American  Association  for  the  Advancement  of  Science, 
Detroit  Meeting,  Aujuet,  1875.]  ,ji 


The  Effect  of  the  Glacial  Epoch  upon  the  Distribution  of 
Iksects  in  North  America.     By  Aug^R^^Gkote,  of  Buffalo, 


N.  Y. 


From  the  condition  of  an  hypothesis,  the  Glacial  epoch  has 
been  elevated  into  that  of  a  theory,  by  the  explanations  it  has 
afforded  to  a  certain  class  of  geological  pheromena.  The  present 
paper  endeavors  to  show  that  certain  zoological  facts  .are  consist- 
ent with  the  presence  in  past  times  of  a  vast  progressive  field  of 
ice  gradually  extending  over  large  portions  of  the  North  American 
Continent  and  moving  from  the  north  to  the  south.  These  facts 
are  in  the  present  instance  afforded  by  a  study  of  the  Lepidoptera, 
certain  kinds  of  butterflies  and  moths  now  inhabiting  the  United 
States  and  adjacent  territories.  Before  proceeding  with  the 
subject,  a  brief  statement  of  some  of  the  phenomena  assumed  to 
have  attended  the  advent  of  the  Glacial  Epoch  is  necessary. 

At  the  close  of  the  Tertiary,  the  temperature  of  the  earth's 
surface  underwent  a  gradual  change  by  a  continuous  loss  of  heat. 
The  winters  gradually  became  longer,  the  summers  shorter.  The 
tops  of  granitic  mountains  in  the  east  and  west  of  the  North 
American  continent,  now  in  summer  time  bare  of  snow  and 
harboring  a  scanty  flora  and  fauna,  became,  summer  and  winter, 
covered  with  congealed  deposits.  In  time  the  mountain  snows 
consolidated  into  glacial  ice  which  flowed  down  the  ravines  into 

(222) 


S-j 


I 


fc^^,-'<^^ 


223 


B.       NATURAL    HISTORY. 


the  valleys.  Meanwhile  the  northern  rejjions  of  the  continent, 
which  may  have  iiiaiignrated,  siihniittcd  cxteiidcdly  to  the  same 
plicnomena.  Glacial  icu,  llrst  made  on  elevations,  linally  formed 
at,  an<l  ponred  over  lower  levels.  Glacial  streams  linally  nnited 
to  form  an  icy  sea  whose  frozen  waters  slowl}'  plowed  the  surface 
of  the  ro(  ks  ;  and  whose  waves,  in  their  movement  from  north  to 
south,  absorbed  the  local  glaciers  in  their  course,  and  extended 
over  all  physical  barriers  into  the  .Southern  States  and  down  the 
Valley  of  tlie  Mississippi.  To  the  main  Ice-sheet,  the  Appalach- 
ians and  Koclv}'  Mountains  are  supposed  to  have  contributed  their 
local  glaciers.  Before  this  frozen  deluge  the  animals  must  have 
always  rctieated.  The  existing  insects  of  the  pliocene  must,  in 
submitting  to  the  change  of  climate  which  accompanied  the  ad- 
vance of  the  glacier,  ha\e  quitted  their  haunts  with  reluctance, 
and  undergone  a  severe  struggle  for  existence,  no  matter  how 
gradually  the}'  had  been  prepared  for  the  encounter.  We  must 
expect  that  nmltitudes  of  specific  forms  ultimately  perished  of 
whose  remains  no  traces  have  been  preserved. 

Such  being  a  brief  statement  of  the  outlines  of  the  opening  of 
the  Glacial  P2poch,  we  turn  to  some  facts  offered  by  a  study  of 
our  existing  species  of  butterflies  and  moths.  Tlie  tops  of  the' 
White  Mountains  and  the  ranges  of  mountain  elevations  in 
Colorado,  offer  us  particular  kinds  of  these  insects  living  in  an 
isolated  manner  at  the  present  day  and  confined  to  their  respec- 
tive localities.  In  order  to  find  insects  like  them  we  have  to  ex- 
plore the  plains  of  Labrador  and  the  northern  portion  of  the 
North  American  Continent,  in  regions  offering  analogous  condi- 
tions to  those  obtaining  on  the  summits  of  these  mountains.  The 
genera  Oeneis  and  Brenthis  among  the  butterflies,  and  Anarta 
and  Agrotis  among  the  moths,  are  represented  by  the  same  or 
similar  species  in  all  of  the  above  mentioned  localities.  In  the 
case  of  the  White  Mountain  Butterfly,  Oeneis  semidea,  we  have  a 
form  sustaining  itself  on  a  very  limited  alpine  area  on  the  top  of 
Mount  Washington. •     Although  there  is  some  doubt  that  precisely 

»  Sec  Mr.  Si'iuMor's  nrticlo  in  tlie  •'  ecology  of  New  Ilampsliire,"  1 ,342.  Mr.  .SciuWer 
first  pointed  ont  the  existence  of  alpine  and  subalpine  fa\inal  belts  on  Monnt  Wa.sliing- 
ton.  and  iutere.sUnjrly  remarks  "  tliat  if  the  .suniniit  of  Jit.  Wasliington  were  somewhat 
less  than  two  thousand  feet  higher  it  would  reach  the  limit  of  perpetual  snow."  Con- 
eult  also,  an  earlier  paper  of  great  value  liy  Dr.  A.  S.  Packard,  Jr.,  on  "The  Insect 
Fauna  of  the  Summit  of  Mount  \Va(:hli)gton  as  compared  wit!  that  of  Labrador"  (these 
rrncecdings.  Vol.  XVI,  1.51).  l>r.  "ackard.  In  ccmiparing  tlio  climate  of  the  two  locali- 
ties. Bays :  "The  seasons  correspon.l  very  exactly,  as  the  snow  melts  in  the  early  sum- 
mer, uud  ice  Ib  formed  early  iu  tlie  autumu  ut  about  the  same  dates." 


.-> 


\ 


I 


.G(^ 


n 


VV 


.J 


B.       NATURAL    IIISTOUr. 


224 


the  same  form  has  been  discovcri'd  in  Colorailo,  the  fact  remains 
tliat  huttertlies  exceedingly  lilu"  it,  tlioiigii  rooistored  by  us  under 
dill'ercnt  specilic  names,  live  in  Lal)rador  and  Colorado. 

■Whether  the  White  ^lountain  Butterlly  be,  as  suspected  by 
Lederer,  a  local  modilication  of  some  one  of  the  Labradoriau 
forms  or  not,  the  geoj5rai)liical  distribution  which  its  genus  enjoys 
cannot  be  meaiungless.  The  question  comes  up,  with  regard  to 
the  White  Mountain  Butterlly,  as  to  the  manner  in  which  this 
species  of  Of'/<e/.s  attained  its  present  restricted  geographical  area. 
How  did  the  White  INIouutain  Butterlly  get  up  the  White 
Mountains  ?  And  it  is  this  question  that  I  am  disposed  to  answer 
by  the  action  attendant  on  the  decline  of  the  Glacial  Epoch. 

I  have  before  brielly  outlined  the  phenomena  attendant  on  the 
advance  of  the  Ice-sheet,  anel  I  now  dwell  for  a  uuunent  on  those 
^vhichmust  equally  be  presumed  to  have  accompanied  its  retire- 
ment.    I>Iany  of   the  features  of  its    advance  were    repeated    m 
reverse  order  on  the  subsidence  of  the  nuiin  Iccsheet  or  Glacial 
sea.     The  local  glaciers  appeared  again  separate  from  the  main 
body  and  filled  the  valleys  and  mountains  and  ravines,  running 
thus  at  variance  with  the  main  body  of  the  C; lacier,  being  deter- 
mined   by   local    topography.      A   reversal   of   the   temperature 
shortened  the  winters  and  Uuigtheued   the  summers.     Ice-loving 
kinds  of  insects,  such  as  our  White  Mountain  Butterfly,  hung  on 
the  outskirts  of  the  main  Ice-sheet,  where  they  found  their  fitting 
conditions  of  temperature   and  food.     The   main   Ice-sheet   had 
pushed  them  insensibly  before  it,  and,  during  the  continuance  of 
the  Glacial   Epoch,  the   geographical   distribution  of  the  genus 
Oeneis  had  been  changed  from  a  high  northern  region  to  one  which 
may  well  have  included  portions  of  the  Southern  States.     And, 
on  its  decline,  the  Ice-sheet  drew  them  back  again  after  itself  by 
easy  stages;  yet  not  all  of  them.     Some  of  these  butterflies 
strayed  by  the  way,  delayed  by  the  physical  nature  of  the  country 
and    destined    to    plant    colonies   forever    separate   from    their 
companions.     Wlien  the  main  Ice-sheet  left  the  foot  of  the  White 
Mountains,  on  its  long  march  back  to  the  pole  where  it  now  seems 
to  rest,  some  of  these  wayward,  flitting,  Oeneis  butterflies  were 
left  behind.     These  had  strayed  up  behind  the  local  glaciers  on 
Mount  Washington,  and  so  became  separate  from  the  main  body 
of  their  companions  which  journeyed   northward,  following   the 
retirement  of  the  main  Ice-sheet.     They  found  in  elevation  their 


i 


r 


•jiil'irflT" 


-v--**  '■* 


»Wifi».T  — W 


/ 


225 


B.      NATURAL    HISTORY. 


congenial  food  and  climate,  and  tliey  have  followed  these  gradu- 
ally to  the  top  of  the  mountain,  which  tlicy  have  now  attained  and 
from  which  tiiey  cannot  now  retreat.  Far  olf  in  Labrador,  the 
descendants  of  their  ancestral  companions  t\y  over  wide  stretches 
of  country,  while  they  appear  to  be  m  prison  on  the  top  of  a 
mountain. 

I  conceive  that  in  ihis  way  the  mountains  generally  may  have 
secured  their  Alpine  animals.  Tlie  Cilacial  Epoch  cannot  be  said 
to  have  expired.  It  exists  even  now  for  high  levels  above  tha 
sea  while  the  Laplander  and  Escpiimaux  find  it  yet  enduring  in  the 
far  North.  Our  yearly  winters  are  fractions  of  the  (ihiciai  year. 
Had  other  conditions  been  favorable,  we  might  now  fnid  Arctic 
man  living  on  snow-capped  mountains  in  tlie  Temperate  zones. 

At  a  height  of  between  5,000  and  0,200  feet  above  the  sea  and 
at  a  mean  temperature  of  about  forty-eight  degrees  during  a  short 
summer,  the  White  Mountain  Butterflies  {Oeneis  semidea),  yet 
enjoy  a  climate  like  that  of  Labrador  witiiin  the  geographical 
limits  of  New  Hampshire.  And' in  tlie  cases  of  the  moths-  an 
analogous  state  of  things  exists.  Tlie  species  Anarta  melanopa  is 
foimd  on  Mount  Washington,  the  Rocky  Mountains  and  Labrador. 
Agrotis  islandica  is  found  in  Iceland,  Labrador,  the  White  Mouti- 
tains,  and,  perhaps,  Colorado.''  As  on  islands  in  the  air,  these 
insects  have  been  left  by  the  retiring  of  the  ice-tlood  during  the 
opening  of  the  Quaternary. 

On  inferior  elevations,  as  on  Mount  Katahdin  in  Maine,  where 
we  now  find  no  Oeneis  butterflies,  these  may  liave  formerly  ex- 
isted, succumbing  at  last  to  a  climate  gradually  increasing  in 
warmth  from  which  they  had  no  escape  ;  ivhile  the  original  coloni- 
zation in  the  several  instances  must  have  always  greatly  depended 
upon  local  topography. 

In  conclusion,  I  have  briefly  endeavored  to  show  that  the 
present  distribution  of  certain  North  American  insects  may  have 
been  brought  about  by  the  phenomena  attendant  on  the  Glacial 
Epoch.  The  discussion  of  matters  connected  with  this  theoretic 
period  of  the  earth's  history,  still,  as  it  now  ap)iears,  brings  out 
more  and  more  a  clearer  conception  of  its  actuality.     I  hope  that 

«I  have  Bince  (Psyche,  1, 131)  recorded  the  first  indication  of  the  occurrence  of  the 
Arctic  Larta  liossii  on  Slount  Washington,  from  a  single  specimen  taken  by  Mr.  B. 
Ficlsman  Mann,  above  tlie  tree  line. 

»I  believe  Dr.  Packard's  id'intiflcation  of  this  species,  in  Prof.  Hayden's  Reports, 
is  Incorrect.    The  Coloradian  species  is  Agrotis  auxiliarU,  Grote. 

A.  A.  A.  8.   VOL.    XXIV.      B.  (15) 


,j*i 
% 


B.      NATnnAt    IIISTOKT. 


22G 


//- 


my  present  statements  may  draw  the  attention  of  our  zoologists 
more  fully  to  the  matter,  seeing  tiiat  we  have  in  our  own  country 
fields  for  its  full  exploration.  And  I  permit  myself  to  believe,  that 
testimony  as  to  the  former  existence  of  a  long  and  widely  spread 
winter  of  the  years,  is  offered  in  evidence  through  the  frail,  l)rown, 
Oeneis  butterflies,  that  live  on  the  tops  of  the  mountains. 


[Printed  at  the  Sai.em  Puess,  June,  187U.] 


